Method of producing crystalline lithium/vanadium oxide powder

ABSTRACT

This invention relates to a method for manufacturing a crystalline powder of a composite lithium and vanadium oxide with formula Li 1+x V 3 O 8 , where x is between 0 and 0.2, comprising: formation of an aqueous suspension starting from an NH 4 VO 3  paste and monohydrated lithia powder; continuous dehydration of this suspension in a hot gas current at a temperature of between 200 and 600° C., to form a dry powder of a precursor with a size grading of between 10 and 100 μm; calcination of this precursor at a temperature of between 380 and 580° C. to form a crystalline powder of Li 1+x V 3 O 8 . The product thus obtained will be used particularly for manufacturing electrodes for lithium rechargeable batteries.

TECHNICAL FIELD

This invention relates to a method for manufacturing a crystallinepowder of a composite lithium and vanadium oxide with formulaLi_(1+x)V₃O₈, where _(x) is between 0 and 0.2. This product will be usedparticularly for manufacturing of electrodes for lithium rechargeablebatteries.

State of the Art

All existing methods for the synthesis of Li_(1+x)V₃O₈ composite oxideuse the reaction of a vanadium compound on a lithium salt. They differdepending on whether or not they use a solvent.

The use of water as a solvent that leads to the formation of a gel isdisclosed in patent US5039582 (PISTOÏA). This gel is obtained from LiOHand V₂O₅ after more than 24 hours, and is difficult to filter and todry. Patent US U.S. Pat. No. 6,177,130 (FREY) describes an aqueoussolution of lithia and vanadium acid prepared by passing ammoniummetavanadate (MVA) on a resin. This solution is dried and its residueredissolved in an organic solvent to generate a product for applicationof an optical quality thin layer. For example, use of the organicsolvent is mentioned in US patent U.S. Pat. No. 5,549,880 (KOKSBANG) andpatent application WO 01/22507 (3M), but there are environment andsafety problems at the industrial stage. Regardless of the solvent type,known methods are discontinuous and limited by the filtration step.

Without a solvent, it is possible to work on a mix of solids. The finalcompound is obtained by melting the mix as described in US patent5013620 (Bridgestone) and in the article by A. D. WADSLEY, Acta Cryst.10 (1957) 261, or a conversion slightly below the melting point asdescribed in U.S. Pat. No. U.S. Pat. No. 5,520,903 (CHANG). Thesemethods introduce the problem of transport and grinding of a material inmolten or sintered blocks.

US patent U.S. Pat. No. 6,136,476 (Hydro-Quebec and 3M) discloses themix of dry powders of a lithium compound and a vanadium compound,grinding by jet, and heating below the melting temperature. The methodenables good control of the size grading in all manufacturing steps,with the number of steps being fairly limited.

However, the solid method has a number of disadvantages compared withthe use of a solvent, which enables a more intimate mix of the reagentsand therefore a more efficient reaction, and easier implementation. Whensynthesizing a crystallized material, crystallisation after solvationcan take place at a lower temperature than with a solid method, which ismore convenient and more economic. Finally, when one of the reagents isobtained in solution, the method with a solvent eliminates a dryingstep.

The purpose of the invention is to provide an almost continuous methodfor manufacturing a crystalline powder of Li_(1+x)V₃O₈, that can beeasily industrialised with a limited number of steps, in which the sizegrading can be controlled in each step, starting from ammoniummetavanadate (MVA) and lithia reagents.

OBJECT OF THE INVENTION

The object of the invention is a method for making a crystalline powderof a composite lithium and vanadium oxide with formula Li_(1+x)V₃O₈,where _(x) is between 0 and 0.2, comprising:

-   -   formation of an aqueous suspension starting from an NH₄VO₃ paste        and monohydrated lithia powder,    -   continuous dehydration of this suspension in a hot gas current        at a temperature of between 200 and 600° C. to form a dry powder        of a precursor with a size grading of between 10 and 100 μm,    -   calcination of this precursor at a temperature of between 380        and 580° C. to form a crystalline powder of Li_(1+x)V₃O₈.

DESCRIPTION OF THE INVENTION

The method begins by putting MVA paste and mono-hydrated lithia powderinto an aqueous suspension, with a mass ratio such that the Li/Vstoichiometry required to give Li_(1+x)V₃O₈ is obtained, where _(x) isbetween 0 and 0.2. The ratio of solids to the total mass is between 40and 60%.

The use of a solvent enables a more intimate mix of reagents and easierimplementation than the solid method. Furthermore, in the special caseof synthesis of a single-phase crystallized material, the solvent methodrequires lower crystallization temperatures than the solid method andtherefore a lower energy cost.

The use of an aqueous solvent has a technical-economic advantagecompared with the method described in US patent 6136476. The inorganicsynthesis procedure of MVA imposes that it should be obtained in the wetstate before calcination or drying. The drying step is not useful andthe MVA (wet, paste or suspension) may be injected into the processdirectly, regardless of whether the MVA used is ultra-pure or is anintermediate product of V₂O₅ in the hydro-metallurgical cycle for theextraction of vanadium in a mining operation. Furthermore, recycling ofthe ammonia effluent may be economically and environmentally attractive,if combined with hydro-metallurgy of vanadium that consumes this gas.

The suspension thus obtained is kept stirred in a neutral atmosphere,for example a nitrogen atmosphere, for between ½ and 24 h and between 20and 90° C., until it is added into a hot gas jet atomiser, for example aRINAJET atomiser made by the RIERA NADEU S.A. company. The strongturbulent flows of hot gases (250-600° C.) from this instrument enableinstantaneous dehydration of the solid product and a precursor of thefinal product is obtained in the form of a dry powder with a sizegrading of between 10 and 100 μm.

The stirred suspension does not have the rheological characteristics ofa gel and the dehydration technology used thus bypasses the difficultfiltration step used by other methods according to prior art using the“sol-gel” method.

The powder obtained is loaded into a belt furnace performing thecalcination step at between 380 and 580° C., avoiding re-agglomerationof the product. This step enables formation of the Li_(1+x)V₃O₈ productcrystallised without degrading the size grading that remains between 10and 100 μm. This product may optionally be micronised and/or mixed withcarbon black.

The method according to the invention enables less discontinuousoperation than other methods using a solvent. The time necessary tocreate a contact in a suspension is shorter than the time necessary toform a gel. Thus, the difficult step of filtration of a gel is avoided,and on the contrary the suspension is dehydrated by continuouslybringing it into a hot gas jet, for example using an instrument in theRINAJET product range (RIERA NADEU S.A.) with a high mass flow.

DESCRIPTION OF THE FIGURES

FIG. 1 shows the diffraction diagram of the final product in example 1.

FIG. 2 shows the diffraction diagram of the final product in example 2.

EXAMPLES Example 1 Standard Purity LiV₃O₈

4872 g of ALDRICH MVA with purity 98.6% (dry weight) and 584 g ofALDRICH LiOH₃H₂O with purity 99.6% were put into suspension in distilledwater, respecting the ratio of 300 ml of solvent per mole of LiV₃O₈.

The approximately 10 litres of suspension thus produced is kept stirredat 50° C. for 24 hours under nitrogen. It is added into a small scalemodel of instruments in the RINOJET commercial range made by the RIERANADEU S.A. company at 1 l/h at a hot gas inlet temperature of 280° C.

The dehydrated powder thus obtained is calcinated in a tray for 10 hoursat 400° C. and the final result is a product identified by X diffractionas being LiV₃O₈ with V₂O₅ as an impurity, for which the most intenseline is at 2θ=20.27°, as shown by the diagram in FIG. 1. Thischaracterisation is made using a Siemens D-5000 diffractometer with theKα line for copper, with 2θ varying from 5 to 100° in steps of 0.02° and2 s per step. The product contains 2.35% of lithium and 52.2% ofvanadium by weight, including 2.21% of V⁺⁴.

Example 2 High Purity LiV₃O₈

The first step is to use an innovative method to make high purity MVA,using 150 kg of VOCl₃ extracted from the applicant's standardproduction. This material is injected into a stirred reactor, into anNH₄OH solution previously prepared from 1 m³ of water and 90 kg ofammonia. The MVA is precipitated by controlling the temperature and thepH, and is washed and filtered on a fabric and is finally discharged inthe form of a wet paste with a humidity of between 30 and 50%.

Two batches of the above method are used to extract 216 kg of highpurity MVA (dry weight) for a wet weight of 336 kg, with the compositionshown in table 1: TABLE 1 Element Cl V⁺⁴ Fe Na Mo K Al Si Ca Zn Mg Cu PbNi Co Content 25 114 6 5 5 3 25 — 7 4 3 3 4 4 <10 (ppm)

31 kg of LiOH₃H₂O produced by the FMC company, dissolved in distilledwater and then mixed with 336 kg of wet MVA, are used to obtain 320 l ofsuspension. Stirring is continued for 24 hours at 4° C. and the productis then added into the S1008 instrument in the RINOJET product rangemade by RIERA NADEU S.A. at 60 l/h at a gas inlet temperature of 350° C.

120 kg of dehydrated powder is recovered from this test, at 80° C. A fewtens of kilograms of the extracted material are calcinated for 10 h at400° C. The size grading of the final product measured by laser sizegrading on an instrument made by Malvern Instruments, is such that 90%of the powder by volume is smaller than 15.3 μm. The X-diffractiondiagram shown in FIG. 2 is the diagram for an Li_(1.2) V₃O₈ crystal withLiVO₃ as the impurity, identifiable by its higher intensity peak at2θ=18.64°. Characterisation is done on a Siemens D-500 diffractometerwith the Kα line of copper, varying 20 from 10 to 70° C. in steps of0.04° with 15 s per step. The composition of the product obtained isgiven in table 2: TABLE 2 Element Li V⁺⁴ Fe Na Mo K Al Si Ca Zn Mg Cu PbNi Co Content 2.9% 51% 40 50 30 40 25 <20 45 5 12 15 <1 20 2 (ppm)

1. Method for manufacturing a crystalline powder of a composite lithiumand vanadium oxide with formula Li_(1+x)V₃O₈, where x is between 0 and0.2, comprising: formation of an aqueous suspension starting from anNH₄VO₃ paste and monohydrated lithia powder, continuous dehydration ofthis suspension in a hot gas current at a temperature of between 200 and600° C. to form a dry powder of a precursor with a size grading ofbetween 10 and 100 μm, calcination of this precursor at a temperature ofbetween 380 and 580° C. to form a crystalline powder of Li_(1+x)V₃O₈. 2.Method according to claim 1, wherein the suspension is stirred beforebeing injected into the hot gas current.
 3. Method according to claim 1,wherein the size grading of the final product is between 10 and 100 μm.4. Method according to claim 1, wherein the NH₄VO₃ paste is a highpurity paste obtained by making VOCl₃ react with NH₄OH.
 5. Methodaccording to claim 2, wherein the size grading of the final product isbetween 10 and 100 μm.
 6. Method according to claim 2, wherein theNH₄VO₃ paste is a high purity paste obtained by making VOCl₃ react withNH₄OH.
 7. Method according to claim 3, wherein the NH₄VO₃ paste is ahigh purity paste obtained by making VOCl₃ react with NH₄OH.
 8. Acrystalline powder produced by a method of claim
 1. 9. A crystallinepowder produced by a method of claim
 2. 10. A crystalline powderproduced by a method of claim
 3. 11. A crystalline powder produced by amethod of claim
 4. 12. An electrode suitable for a lithium rechargeablebattery comprising a powder of claim
 8. 13. An electrode suitable for alithium rechargeable battery comprising a powder of claim
 9. 14. Anelectrode suitable for a lithium rechargeable battery comprising apowder of claim
 10. 15. An electrode suitable for a lithium rechargeablebattery comprising a powder of claim
 11. 16. A battery comprising apowder of claim
 8. 17. A battery comprising a powder of claim
 9. 18. Abattery comprising a powder of claim
 10. 19. A battery comprising apowder of claim
 11. 20. A Li_(1+x)V₃O₈ crystallized powder having a sizefrom 10 to 100 μm that has been prepared without filtration of a gel.